Crushed Rock Samples Research Articles

A DEM-CFD Approach for Predicting Pressure Drop Through Packed Bed of Crushed Rocks

Predicting the pressure drop over a packed bed of air-crushed rocks is a crucial parameter for a solar storage system to be economically viable. The selection of the blower and the estimation of the total capacity of the storage system are highly dependent on it. There are various parameters that influence the air flow through the bed, such as the shapes and sizes of the crushed rocks, which affect the packing density and particle arrangement. In this paper, the crushed rock was represented by an ellipsoidal shape with the same volume and aspect ratio as the average of randomly collected crushed rock samples to investigate the pressure drop through the packed bed. Simulation models were developed to assist in driving a pressure drop correlation as well as the effect of particles' orientation on pressure drop. For simulation, a Discrete Element Model (DEM) was used to generate the particles and Computational Fluid Dynamics (CFD) to simulate the flow over the particles. To validate the DEM/CFD models, experiments consisting of a packed bed of ellipsoidal particles and crushed rocks were developed. Consequently, an equation based on the porous media approach was proposed to predict the pressure drop, and the correlation was found to underestimate the pressure drop through the crushed rock by less than 20% in the horizontal flow.

Laboratory experiments and modelling of the geochemical interaction of a gabbro-anorthosite with seawater and supercritical CO2: A mineral carbonation study

The potential for mineral carbonation of carbon dioxide (CO2) in a plutonic mafic rock is addressed in this work through a set of laboratory experiments on a gabbro-anorthosite sample from the Torrão - Odivelas Massif (Portugal). The experiment was conducted in two stages under pressure (8 MPa) and temperature (313.15 K) conditions similar to those expected around a CO2 injection well. Stage-I simulated dissolution conditions, with a crushed rock sample (1–3 mm) exposed for 30 days to CO2 supersaturated seawater (0.576 M). Stage-II favoured carbonation conditions; cubic rock specimens (8 cm3) were brought in contact with the Stage-I seawater subsaturated in CO2 (0.095 M).A multi-analytical methodology was applied to follow the mineralogical and geochemical evolution of rock and seawater during both stages. At the end of Stage-I, the aqueous phase showed a marked increase in iron (Fe), magnesium (Mg) and calcium (Ca) ions and milder increase in silicon (Si) and aluminium (Al) ions. At the end of Stage-II, a decrease in Si and Al concentrations was observed while the Fe, Mg, Ca concentrations still increased, albeit at a lower rate. No significant geochemical variations were detected in the bulk solid phase. The bulk X-ray diffraction (XRD) analyses detected halite as a new mineral phase, while the grazing-XRD design revealed the presence of dolomite. Moreover, the elemental distribution mapping demonstrated the spatial association of carbon with magnesium indicating magnesite crystallisation. The geochemical model developed in CrunchFlow code was able to reproduce the experimental observations and simulate the chemical behaviour for longer time periods.Overall, the experiments and model point towards a mineral carbonation potential in the Torrão - Odivelas Massif, with further studies being required to upscale the laboratory results to field scale.

Experimental determination of gas-water relative permeability for ultra-low-permeability reservoirs using crushed-rock samples: Implications for drill cuttings characterization

Relative permeability controls fluid flow through rocks, with applications to hydrocarbon production, geologic carbon and energy storage. However, significant challenges are associated with the measurement of relative permeability for rocks with matrix permeability in the microdarcy to nanodarcy range. The primary objectives of this study are therefore to 1) propose an integrated experimental and modeling approach for gas relative permeability (krg) evaluation using crushed-rock samples and 2) perform a proof-of-concept study to demonstrate that gas–liquid relative permeability can be determined for ultra-low-permeability (unconventional) reservoir samples that have been crushed to certain grain sizes (20–35 mesh size).In this study, the water vapor ad-/desorption technique was employed to provide a wide range of water saturations (Sw). The evolution of water distribution in the shale matrix with a change in Sw was investigated by using a modified low-pressure adsorption (LPA) technique. A recently-developed numerical model was modified to estimate effective permeability to gas at each saturation level. Four clay-rich shales from the Duvernay (Canadian) and Kyalla (Australian) formations were analyzed.The vapor ad-/desorption technique provided an efficient approach to saturate the studied samples. By changing relative humidity in sealed desiccators using different salt solutions, a maximum Sw of 83% was obtained for organic-matter rich samples, and 99% for organic-matter lean shales. As interpreted using the modified LPA technique applied at different saturation levels, water is held in films in mineral-associated macro-/mesopores, and can block access to organic-matter pores through the formation of water clusters, significantly reducing the accessible organic-matter porosity and gas effective permeability. Imbibition krg decreases rapidly and significantly (over 90%) when Sw reaches approximately 0.3–0.4 for samples containing significant amounts of water-sensitive clay minerals (Kyalla #2) and TOC (Duvernay #2). Relative permeability hysteresis occurs for Duvernay #2 and Kyalla #1. Overall, the use of crushed-rock samples (non-matrix/fracture system), and application of the vapor sorption technique, results in a small amount of hysteresis.A laboratory-based method for measuring gas relative permeability of ultra-low-permeability reservoirs using crushed-rock samples is provided for the first time, with important applications to the energy and carbon capture industries.

Hydrogen generation in crushed rocks saturated by crude oil and water using microwave heating

Fossil-based hydrogen (H2) production, such as steam methane reforming (SMR), typically occurs at surface facilities using hydrocarbons as a major feedstock. Such approach generates significant amount of byproduct carbon dioxide (CO2) and requires the costly carbon capture and geological storage. Here we propose a novel approach to generate hydrogen within petroleum reservoirs using the remaining/unrecovered oil and gas. To validate this scientific proof-of-concept, we use microwave (MW) heating to initiate the reactions of crude oil, water, and/or catalysts in crushed rock samples. A maximum of 63% ultimate hydrogen content is obtained in generated gas mixtures, while CO2 is always less than 1%. Besides hydrocarbon cracking, additional hydrogen is generated by water-gas shift reactions. Water-oil ratios in rocks also affect hydrogen yield, with 1:1 appearing as an optimal ratio. Furthermore, we find that iron catalysts can accelerate reaction rate but has limited effects on ultimate hydrogen yield. Metal minerals in rocks may act as natural catalysts to enhance hydrogen generation. Overall, this work demonstrates the technical feasibility of in-situ hydrogen generation directly from petroleum reservoirs.

Advances in carbon isotope analysis of trapped methane and volatile hydrocarbons in crystalline rock cores.

The isotopic composition of hydrocarbons trapped in rocks on the microscale (fluid inclusions, mineral grain boundaries, microfractures) can provide powerful information on geological and biological processes but are an analytical challenge due to low concentrations. We present a new approach for the extraction and carbon isotopic analysis of methane (CH4 ) and hydrocarbons in trapped volatiles in crystalline rocks. An off-line crusher with cryogenic trapping and a custom-made silica glass U-trap were attached to an external injector port on a continuous flow gas chromatograph/combustion/isotope ratio mass spectrometer to demonstrate the accuracy, reproducibility, and sensitivity of δ13 C measurements for CH4 . The method can isotopically characterize CH4 in crushed rock samples with concentrations as low as 3.5 × 10-9 mol/g of rock, and both sample and isotopic standards are analyzed with an accuracy and reproducibility of ±0.5‰. High H2 O/CH4 ratios of 98 to 500 have no effect on measured δ13 CCH4 values. The method is successfully applied to natural samples from the north range of Sudbury Basin, Ontario, Canada. The δ13 C isotopic signatures of CH4 trapped microscopically in rock from the north range overlap significantly with that of CH4 contained in larger scale flowing fracture fluids from the same part of the Sudbury Basin, indicating a potential genetic link. A novel method for δ13 CCH4 analysis was developed for the extraction of nanomole quantities of CH4 trapped microscopically in rocks. The technique has an accuracy and reproducibility comparable to that of on-line crushing techniques but importantly provides the capability of crushing larger rock quantities (up to 100 g). The benefit is improved detection levels for trace hydrocarbon species. Such a capability will be important for future extension of such crushing techniques for measurement of 2 H/1 H for CH4 , clumped isotopologues of CH4 and other trapped volatiles species, such as C2 H6 , C3 H8 , C4 H10 , CO2 and N2 .

Експериментальні дослідження деформаційних характеристик закладальних масивів

Purpose of work is to determine the deformation characteristics of the backfill massifs used to support the side rocks behind the working face in the cut area of a coal mine. To achieve this goal, laboratory studies were carried out on samples of crushed rock of different particle-size composition, which were subjected to uniaxial compression in a steel cylinder (virgin compression) and in a special bag (with the possibility of lateral expansion of the filling material). As a result of the studies performed, it was found that the relative deformation of a compacting body from crushed rock during virgin compression is less than the relative deformation of the same body when lateral expansion of the filling material is possible. It has been experimentally proven that with the possibility of lateral expansion of the filling material, the values of the relative deformation change according to a linear relationship, when with an increase in the bulk density of crushed rock after uniaxial compression, a decrease in the vertical size of the compacting body is recorded. For crushed rock of heterogeneous particle-size composition, at maximum values of the compaction coefficient and virgin compression, the vertical size of the compacting body is 36 % less than in the case of uniaxial compression of the filling material with the possibility of lateral expansion of the crushed rock. Moreover, the smaller the fraction of crushed rock, the greater the recorded difference. The change in the cubic capacity of the compacting body occurs as a result of repackaging of particles of different sizes in the total volume of the filling material and the spread of crushed rock along the plane under the action of a compressive load. The value of Poisson’s ratio under conditions of uniaxial compression of crushed rock with the possibility of lateral expansion of the compacting body changes according to a parabolic dependence and reaches minimum values in the presence of inhomogeneous (in particle size) crushed rock in the filling material. The maximum values of the investigated coefficient are provided after compression of the initial material of coarse or fine fractions, which initially compose the filling mass. Ensuring the stability of side rocks, the operational state of mine workings in the excavation areas of a coal mine and preventing subsidence of the earth's surface are achieved after the construction of a filling mass in the worked-out space, consisting of inhomogeneous (in size) pieces of crushed rock, which has compression characteristics. Therefore, the requirements for the properties of filling arrays are determined in accordance with their purpose.

Surfactant-EOR in tight oil reservoirs: Current status and a systematic surfactant screening method with field experiments

Tight oil reservoirs typically have an estimated ultimate recovery of less than 10% after hydraulic fracturing, where enhanced oil recovery (EOR) technique is needed. Comparing to the gas-EOR, the surfactant-EOR neither alters the current fracturing procedure nor requires special injection facilities, and thus can be economically-viable under the current environment of low oil prices. However, tight rocks have small pores and large specific surface areas, which can make the adsorption rate of surfactants significant and thus limit the penetration depth of surfactants and its enhancement on oil recovery. In the published studies on the surfactant-EOR for shales and other tight reservoirs, this key parameter is only measured with the crushed rock samples, which can be underestimated comparing to that in the intact rock. Moreover, the dispersion coefficient that determines the penetration speed of a surfactant has never been directly measured in the tight rock, and the potential interaction between the surfactant and the friction reducer has neither been studied. In this study, a new form of surfactants is introduced, in which the wettability-alteration surfactants are firstly synthesized into oil-in-water microemulsions and then diluted to a designed concentration in the fracturing fluid. The thermodynamically-stable structure of microemulsion can minimize the adsorption rate of surfactants when transporting in the tight rock. Using coreflood experiments with UV–vis spectroscopy, the adsorption rate and dispersion coefficient of this form of surfactants are directly measured in tight rocks with a range of permeabilities, which are key parameters to modeling the EOR process and further scaling up laboratory findings for designing a field operation. To ensure the success of the surfactant-EOR technique in the field, the chosen surfactant needs to pass the preliminary screening including the aqueous stability test, the emulsion tendency test, the oil-water IFT measurement, and the shearing test; besides, it is also crucial to examine the compatibility between the slickwater and the wettability-alteration surfactant with different electric charges, which is seldom reported yet. In the end, the chosen surfactant is tested in two pairs of horizontal wells on one pad site, whose flowback water is collected and analyzed for better understanding the behavior of this surfactant.

Matrix permeability measurement from fractured unconventional source-rock samples: Method and application

Shale matrix permeability is one of the most important parameters for characterizing a source rock reservoir and for predicting hydrocarbon production. The low permeability value and the presence of induced fractures during core retrieval and transportation make the accurate measurement of the true permeability values for source rocks a significant challenge for the industry. The steady state flow method and the transient pressure pulse decay method on core plug samples mainly measure the permeability of fractures when fractures are present. While the Gas Research Institute (GRI) method that uses pressure decay on crushed rock samples was designed to overcome this difficulty associated with the induced fractures, its measurement results are reported to be sensitive to the particle size of crushed rock samples and also need correction of Knudsen diffusion effect. Moreover, the GRI method is limited to the unconfined stress condition.This work develops a practical method to measure the matrix permeability values from fractured source rock samples by extending the commonly used pressure pulse decay method. A source rock sample with fractures can be more accurately described by a dual-continuum system consisting of a fracture continuum and a matrix continuum. During the pulse decay test, the initial flow across the source rock sample is dominated by the fracture continuum because it has much higher permeability values than those for the rock matrix. Thus, the initial gas pressure signals from the test are used to estimate the fracture permeability. During the late-stage of a pulse decay test, the flow process within the rock sample is controlled by the rock matrix. The observed pressure signals at this stage are used for estimating matrix permeability. The method is based on the analytical solution to gas flow in the fractured rock sample and relatively simple to apply in practice. Both fracture and matrix permeability's dependence on the effective stress can be assessed with this method.

Оцінка стійкості гірничих виробок при ударних навантаженнях

Purpose of work. The purpose of the research is to determine the conditions for ensuring the stability of mine workings in the coal massif under the action of shock loads. Methods. To achieve this goal, analytical studies were performed using the basic provisions of classical mechanics and the theory of elasticity. In laboratory studies, experimental samples of crushed rock were used, which were placed in a steel cylinder. Results. In the course of experimental research, the influence of the impact force and the impact pulse of the falling load on the response of the plane on a pliable basis with inhomogeneous, piece-sized, fragmented rock was studied. It is recorded that at a constant amount of energy of a single impact (mgH = 14.7 J), when the height of the fall of the load decreases 3 times (from H = 1.5 m to H = 0.5 m), and the mass increases from m = 1.0 kg to m = 3.0 kg, the magnitude of the impact force is reduced by 50%. With an increase in the amount of energy of a single impact (from mgH = 4.9 J to mgH = 44.1 J) at the same height of fall, when the mass of the load increases threefold, there is an increase of 2.5 times the impact force. At a constant amount of energy of a single impact (mgH = const), the displacement of the plane on a pliable base of crushed rock depends on the magnitude of the impact pulse of the falling load. Novelty. It is proved that when there is collapse of lateral rocks in the coal massif containing the production, the force of impact on the surface is proportional to the time of fall of the rock blocks to the time of their impact interaction with the plane. Practical significance. In deep coal mines, as a result of mining and the probability of shock loads from landslides, to ensure the stability of mine workings in excavation sites, it is advisable to use pliable supports or filling the produced space with crushed rock, which will ensure the integrity of lateral rocks.

The effects of high temperature on the compaction behaviour of waste rock backfill materials in deep coal mines

To study the mechanical properties of backfill materials during compaction at high ground temperature in deep backfill mining, the WAW-1000D electro-hydraulic servo universal machine was used to conduct compaction testing of crushed sandstones heated to different temperatures. The stress–strain curves of crushed sandstones with four particle sizes heated to different temperatures were obtained. In this way, this study analysed the influence of temperature on the stress–strain relationship, porosity changes, and deformation mechanisms during the compaction of crushed sandstones. The experimental results demonstrate the following: (1) At the same particle size, with increased heating temperature, the strain in crushed waste rock decreased at a given applied stress. (2) After heating to the same temperature, the final strains in crushed waste rock samples of different particle size distributions decreased with particle size. (3) As heating temperature increased, the porosities of crushed waste rock samples heated to 100 °C, 200 °C, 300 °C, and 25 °C are ranked thus (in descending order) at the same stress. (4) After compaction of the samples at 25 °C, the number of large blocks decreased, while that of smaller blocks increased slightly. After compaction of heated samples of crushed waste rock, the amount of large blocks gradually reduced, while that of medium- and small-sized blocks gradually increased with increasing temperature. The temperature affects the deformation mechanisms during compaction of the samples of crushed waste rock, thus affecting their stress–strain relationships and porosity.

Introduction to Rock and Soil Abrasivity Index (RSAI)

Characterizing the abrasiveness of rock and soil and developing predictive models for wear of various tools that interact with such geo-materials is critical in selection of best tool materials for applications in earthmoving, drilling, mining, construction, tunneling, and agricultural industries. This paper introduces a Rock and Soil Abrasivity Index (RSAI), utilizes the abrasive wear theory for defining the parameters and examines a testing method for quantitative assessment of the index. The test method measures the wear mass of a target tool material (i.e. steel or hard facing) while it is pressed against the crushed rock or soil medium in a relative motion under high contact stresses based on a defined test protocol for reliability and repeatability. The RSAI is defined as the product of wear volume and hardness of tool divided by the work or energy deployed to overcome frictional forces, as measured by the torque in the device. The RSAI is expected to vary in the 0–100 range for the softest to the hardest possible rock and soil samples and conditions. The RSAI for various soil and crushed rock samples were experimentally determined and presented. Also, the correlation between the RSAI, Cerchar Abrasion Index (CAI) and Soil Abrasion Test (SAT) value, as the most common forms of abrasion testing of soil and rock is discussed.

A new low-permeability reservoir core analysis method based on rate-transient analysis theory

Unconventional reservoirs such as shales (mudrocks) and coals may exhibit an ultra-low matrix permeability (<0.001 md) challenging conventional laboratory-based methods for permeability measurement. Small-diameter core plug or crushed rock samples, combined with unsteady-state methods, are currently favored to reduce measurement times for ‘tight’ rocks. For core plug analysis, unsteady-state pulse-decay permeability (PDP) or steady-state methods (SS) are commonly employed in commercial laboratories, with the core plug sample subjected to confining stress. Analysis times, particularly for SS methods, may be excessive for ultra-low permeabilities in the nanodarcy range. Another limitation of both PDP and SS experiments applied to core plugs is that they do not represent the boundary conditions typically used to produce hydrocarbons from unconventional reservoirs in the subsurface through wells.Rate-transient analysis (RTA) is a technique used to quantitatively analyze production data from wells drilled into unconventional reservoirs to extract reservoir (e.g. permeability, hydrocarbons-in-place) and hydraulic fracture (conductivity, fracture length) properties. Multi-fractured horizontal wells (MFHWs) producing from low-permeability reservoirs commonly exhibit the flow-regime sequence of transient linear flow, where hydrocarbons flow through the reservoir orthogonal to hydraulic fractures or the horizontal well, followed by boundary-dominated flow caused by pressure interference between adjacent hydraulic fractures or wells. Transient linear flow may be analyzed using RTA methods to extract fracture or well-length (if permeability is known); the end of linear flow can be used to estimate permeability of the reservoir, and boundary-dominated flow to estimate hydrocarbons-in-place.In this work, a new experimental procedure and set-up, applied to core plugs under stress conditions, is developed to mimic well operating conditions encountered in the field (i.e. producing from a subsurface unconventional reservoir). After injection of methane gas into one end of the core plug, and pressure stabilization, the gas is flowed out of the same end of the core plug at constant pressure (with the aid of a backpressure regulator), and flow rates are measured with a flow meter. This procedure is applied to a core plug extracted from a low-permeability siltstone of the Montney Formation (western Canada). Repeated testing consistently demonstrated a transient linear flow period, as the gas pressure transient propagated along the core plug, followed by boundary-dominated flow after the pressure transient reached the end of the core plug; this sequence is identical to what is commonly observed in the field. Permeability was estimated using both the slope of a square-root of time plot (a common RTA method used to analyze transient linear flow), and the time at the end of linear flow combined with the linear flow distance of investigation (DOI) equation. Permeability from both techniques is in good agreement (±5% for both experiments performed), providing an important redundancy to the analysis procedure. Pore volume (and hence porosity, with bulk volume known) may be estimated from the time at the end of linear flow and the slope of the square-root of time plot – the calculated value is in excellent agreement (±2% for both experiments performed) with that obtained from pore volume/porosity estimates using a helium pycnometer (combined with calipered dimensions). Finally, test times for the ∼0.0007 md core plug sample, after the initiation of the production phase, are on the order of only a few minutes to obtain the two independent estimates of permeability and pore volume, which is faster than that achievable from a PDP test.The new innovative experimental procedure is successful in reproducing the physics of flow in unconventional reservoirs, with the results being analyzable with the same techniques applied to field data.

Permeability estimate of underground long-wall goaf from P-wave velocity and attenuation by lab-scale experiment on crushed rock samples

In this study, forty-five crushed rock samples were formed from rock and coal particles of different sizes to simulate the crushed and fragmented condition of a goaf area in an underground coal mine. The porosity (φ) range of the crushed samples was based on field observations in actual goafs. The permeability (k) was measured by reducing the size of the fragments of the actual goaf to lab-scale particles. Ultrasonic wave velocity (VPG) and attenuation (β) were measured for different porosities, particle sizes and frequencies. The ratio of the seismic wavelength and particle size was adjusted to match that of the parameters in the goaf. The results showed that the measured permeability conformed to the Kozney-Carman (KC) equation with a percolation threshold porosity of 0.06. The permeability of the crushed rock was dependent on φ4. The variations of the seismic velocity (η) and attenuation (ξ) were defined based on the ratio of the seismic parameters of the crushed rock and intact rock. η showed a linear relationship with the square root of the tortuosity (τ) for τ = 5–10. ξ showed an approximately linear relationship with the porosity part of the KC equation. An empirical equation is proposed based on the KC equation, involving the seismic velocity, attenuation and particle size. The estimated permeability based on the modified KC equation showed good agreement with the measured data. The permeability of the actual goaf was estimated as 1.0 × 104–6.5 × 105 d based on the rock properties in the goaf.

Experimental investigations of SDS adsorption on the Algerian rock reservoir: chemical enhanced oil recovery case

The adsorption of surfactant on reservoir rocks or sands is one of the main factors that can significantly reduce the effectiveness of surfactant flooding for light oil recovery. The present work consists of study of the interaction between the surfactant sodium dodecyl sulfate (SDS) and the characteristics of Hassi Messaoud rock established using scanning electron microscopy, Fourier transform infrared analysis, Brunauer–Emmett–Teller surface area analysis and optical microscopy. Parametric study of the adsorption tests was carried out at a temperature between 25 and 80 °C. The conductivity method was used to measure the critical micellar concentration of the SDS surfactant in aqueous solutions. The adsorption data were adjusted using five isotherms and two kinetics of the anionic surfactant. The equilibrium conditions for crushed rock samples were obtained after 11 h of adsorption. According to the experimental results, the equilibrium data were well fitted by the Langmuir isotherm for sandstone sample at all temperatures. The pseudo-second-order model best describes the kinetics of the adsorption process. Furthermore, the adsorption process is exothermic. Several statistical error analyses were applied to evaluate the performance and accuracy of the proposed experiment. A systematic investigation is very useful for selecting an appropriate surfactant for enhanced oil recovery application and reservoir stimulation in the petroleum industry.

Application of Hydraulic Flow Unit for Pore Size Distribution Analysis in Highly Heterogeneous Sandstone Reservoir: A Case Study

Verifiable and accurate prediction of reservoir pore sizes from well logs in a well with no previous exposure of core data is the desirable outcome for any technique intended to estimate pore size. Many methods are based on core and crushed rock samples such as thin section analysis, scanning electron microscope (SEM) and mercury intrusion capillary pressure (MICP) to characterize pore features but these methods are not commonly used because of their high cost. This study introduces a cost-effective approach to establish a relationship between hydraulic flow unit and pore size distribution using routine core analysis data and geophysical well logs. Multi-parameter cluster analysis is used to classify the reservoir rock volume into hydraulic flow unit with similar rock characteristics using reservoir quality index (RQI) and flow zone indicators. Well log and core analysis data were used to identify the hydraulic flow unit in the reservoir interval. The discriminant approach was then applied to the predicted hydraulic flow unit to access the range of pore sizes. The predicted hydraulic flow unit with high porosity and permeability and high RQI revealed a range of pore sizes (macro and mega pores). Comparing the obtained results with high-resolution rock thin section study and available empirical approaches indicated verifiable and satisfactory results. The study can extrapolate the pore size information vertically as well as in the neighboring wells in a quite simple and economical way.

Investigation of the mechanical properties and carbonation of construction and demolition materials together with rubber

One of the ways to improve the strength properties of construction and demolition (C&D) wastes is to adopt the accelerated carbonation technique. The main objective of this study was to evaluate the effects of the eco-friendly carbonation approach on the mechanical properties of C&D aggregates together with crumb rubber. Crumb rubber with particle sizes ranging from 400 to 600 μm was added to the 20 mm recycled concrete aggregate (RCA) and crushed rock (CR) at 0.5, 1, and 2% by weight percentage of the aggregates. Then, the unconfined compression strength (UCS) and resilient modulus (Mr) tests were conducted on the carbonated RCA and CR samples together with crumb rubber, and the results were compared with those of the uncarbonated specimens. The results showed that the carbonation process led to a significant increase in the UCS values. However, carbonation resulted in a decrease in the deformability of the specimens compared with the uncarbonated specimens. Moreover, carbonation resulted in a significant increase in the Mr values compared with those of the uncarbonated values. Also, the carbonation process had a more substantial effect on the Mr values of the CR than of the RCA.

Permanent deformation behaviour of pavement base and subbase containing recycle concrete aggregate, coarse and fine crumb rubber

Pavement layers must be sufficiently strong to carry all traffic loads and resist the accumulation of permanent deformations such as rutting and avoid premature failures including top-down cracking during their service lives. In recent years, the utilization of recycled construction and demolition (C&D) materials in civil and transportation infrastructure construction has been considered as a significant solution to replace conventional and natural aggregates, therefore to achieve the goal of building low-carbon footprint constructed facilities. Unfortunately, limited data have yet reported on the permanent deformation behaviour of the recycled materials in pavement, especially the effect of crumb rubber and rubber size with C&D aggregates on the permanent deformation behaviour in base and subbase layers. This paper provides unique laboratory information and testing results in this regard. In this study, two different groups of crumb rubber particles with sizes ranged from 400 to 600 µm (fine) and 15–20 mm (coarse) were separately added to 20 mm recycled concrete aggregate (RCA) and 20 mm crushed rock (CR) at 0.5, 1 and 2% by weight of the aggregates to study the effects of crumb rubber and rubber size on permanent deformation behaviour of RCA and CR aggregates. In particular, the permanent deformation behaviour of the RCA/CR with crumb rubber was investigated through the repeated load triaxial tests. It was observed that the CR samples should be avoided for use in base and subbase courses.

Lithological classification and chemical component estimation based on the visual features of crushed rock samples

Lithological classification and monitoring of ore quality are challenging issues in mine operation, especially to maintain desired feed for processing minerals plants. Quantification of visual features is an innovative method to analyze rock components. In this paper, an analysis of vision-based rock type and classification algorithm is proposed for fast, inexpensive, and reliable identification process compared with common chemical analysis. To evaluate the proposed algorithm, samples were collected from the Novin limestone mine in Iran. Based on chemical and thin-section studies, the samples were classified into three different groups as calcium carbonate, dolomite, and dolomitic limestone. The limestone samples were crushed, sieved, and, respectively, divided into three size fractions as 2.5–7, 1.5–2.5, and 0.1–1.5 cm. A set of 58 images as large and medium size samples and 78 images as fine size samples were taken in the laboratory environment. Features were extracted from the captured images and reduced by applying principal component analysis (PCA). The support vector machine (SVM) and Bayesian techniques were used for classification. The best classification accuracy was about 80 and 90% in limestone and dolomite rock samples, respectively. Then, a multi-layer perceptron (MLP) neural network was employed to predict chemical compositions percentages. The determination coefficient within the range of 0.76 to 0.85 was observed and predicted values confirmed good performance of the grade estimation. The outputs illustrated that the proposed intelligent and automated technique can be successfully applied to monitor ore grade and classify lithology in different stages of mining projects.

Petrophysical interpretation of laboratory pressure-step-decay measurements on ultra-tight rock samples. Part 1 – In the presence of only gas slippage

Conventional laboratory characterization of ultra-tight reservoir rock samples involves separate laboratory measurements on different core plugs or on crushed rock samples. Heterogeneity and anisotropy of ultra-tight reservoir samples adversely influence the laboratory correlation among various measured and estimated petrophysical properties. We apply an inversion algorithm to simultaneously estimate the intrinsic permeability (ki), effective porosity at ambient condition (ϕ0), pore-volume compressibility (Cp), and Klinkenberg-slip factor (b) of an ultra-tight pyrophyllite sample from a single laboratory-based pressure-step-decay measurement.The inversion algorithm is valid for nitrogen injection pressure in the range of 50–500 psi. The algorithm assumes ideal-gas behavior of the injected nitrogen, 1D isothermal laminar gas flow, homogeneity of the core, pressure-independent gas viscosity, inverse-pressure dependence of the apparent permeability, pressure-independent Klinkenberg-slip factor, non-negligible pore-volume compressibility, pressure-dependent effective porosity, negligible inertial effects, square of pressure gradient is significantly smaller than pressure times second derivative of pressure along the entire length of the core plug, and time-invariant confining pressure.Parameter-estimation results based on the proposed inversion scheme are shown to be independent of the values of the initial guess for ki in the range of 1 nd to 10 μd, ϕ0 in the range of 0.01–0.20, Cp in the range of 10−2 to 10−6 psi−1, and b in the range of 0–200 psi. Estimated apparent permeability and effective porosity of the pyrophyllite samples exhibit strong pore-pressure dependence; consequently, both the properties vary substantially along the sample length during the pressure-step-decay measurement. The pyrophyllite samples studied in this work are assumed to be homogeneous. The numerical model of the pressure step decay measurement accounts for the variation in porosity and permeability along the length of core due to the time-dependent pore pressure variation during the experiment. On an average, the effective porosity of the pyrophyllite samples increased by 100% and the apparent permeability decreased by 75% when the pore pressure increased from 50 psi to 500 psi during the measurement. The average values ki, ϕ0, Cp, and b of the nine pyrophyllite samples were estimated to be 40 nd, 0.03, 2 × 10−3 psi−1, and 100 psi, respectively.

Dynamic simulation of CO2-injection-induced fault rupture with slip-rate dependent friction coefficient

Poro-elastic stress and effective stress reduction associated with deep underground fluid injection can potentially trigger shear rupture along pre-existing faults. We modeled an idealized CO2 injection scenario, to assess the effects on faults in the first phase of a generic CO2 aquifer storage operation. We used coupled multiphase fluid flow and geomechanical numerical modeling to evaluate the stress and pressure perturbations induced by fluid injection and the response of a nearby normal fault. Slip-rate dependent friction and inertial effects have been taken into account during rupture. Contact elements have been used to take into account the frictional behavior of the rupture plane. We investigated different scenarios of injection rate to induce rupture on the fault, employing various fault rheologies. Published laboratory data on CO2-saturated intact and crushed rock samples, representative of a potential target aquifer, sealing formation and fault gouge, have been used to define a scenario where different fault rheologies apply at different depths. Nucleation of fault rupture takes place at the bottom of the reservoir, in agreement with analytical poro-elastic stress calculations, depending on injection-induced reservoir inflation and the tectonic stress scenario. For the stress state considered here, the first triggered rupture always produces the largest rupture length and slip magnitude, both of which correlate with the fault rheology. Velocity weakening produces larger ruptures and generates larger magnitude seismic events. Heterogeneous faults have been considered including velocity-weakening or velocity strengthening sections inside and below the aquifer, with the upper sections being velocity-neutral. Nucleation of rupture in a velocity-strengthening section results in a limited rupture extension, both in terms of maximum slip and rupture length. For a heterogeneous fault with nucleation in a velocity-weakening section, the rupture may propagate into the overlying velocity-neutral section, if the extent of velocity-weakening and associated friction drop are large enough.